Welsh finance minister Edwina Hart has claimed the Assembly has been let down by architects over the construction of its ill-fated headquarters.

Mrs Hart said the firm which designed the HQ should have known it could not be built to budget.

She said there were 'over 100' instances of cost and work being underestimated on the project, which saw architect Lord Richard Rogers sacked for the first time in his career.

In the latest chapter in the row between the two, Mrs Hart refutes the world-renowned peer's claims that she had misled the Assembly over the project and said it was time to set the record straight.

In a nine-page confidential letter sent to all AMs, and seen by PA News, Mrs Hart said: 'I feel that the Assembly has been badly let down by the Richard Rogers Partnership.

'I had not wanted to be drawn into public disputes with Lord Rogers about blame, but his allegations have made it necessary to set the record straight.

'However, I believe that it is now more important to concentrate on the way forward and on securing an Assembly building that will fulfil our needs at an acceptable cost.'

Mrs Hart 'utterly' refuted Lord Rogers' claims that she had ignored warnings over the rising costs of the project and that he had been denied the chance to state his case.

And she said the architect knew his cost plan was lacking.

'(It) begs the question why RRP (Richard Rogers Partnership) chose to submit a cost plan which they apparently thought was likely to prove deficient in at least two respects and which would prove deficient in a third if the Assembly's aspiration, clearly expressed in the project brief, to make appropriate use of Welsh materials was to be realised,' she said.

'Inclusion of increased costs under these heads would certainly not have supported a contention that the scheme design was 'within budget'.'

Mrs Hart said her advisers discovered the majority of the cost increase was down to underestimates in the November 2000 cost plan.

They identified more than 100 instances of underestimates of the costs, scope and/or content of work.

They also said the scheme design presented by RRP could not have been built within the cost plan it presented at that time and RRP 'should have known that'.

The letter comes after Mrs Hart last week insisted Lord Rogers could be brought back on board to build the HQ.

She also revealed the Assembly's audit committee could carry out another investigation into the debacle.